Many methods of welding are known in the art, each with its own advantages and disadvantages. Common welding processes include gas welding, oxyacetylene brazing and soldering, shielded metal arc welding (SMAW) or "STICK" welding, metal inert gas (MIG) or "wire feed" welding, gas tungsten arc welding (GTAW) or "TIG" welding, and plasma cutting. TIG welding is perhaps the cleanest, most precise of all hand-held welding operations. Although the method and apparatus of the present invention is preferably directed to a TIG welding operation, one skilled in the art will appreciate that the present invention may have applications for many other welding processes.
A TIG welding process will now be described with reference to FIG. 1. In TIG welding, a concentrated high-temperature arc is drawn between a non-consumable tungsten electrode 10 and a workpiece 14, workpiece 14 being connected to the output of a welding power source (not shown) via a work clamp 24. Electrode 10 rests in a torch 16, the torch including a protective gas source 18, such as a cup, to direct a protective gas 20, such as argon, helium, a mixture thereof, or other inert or non-inert gasses, to a welding site 22 on workpiece 14. Torch 16 receives a flow of protective gas 20 from a gas tank (not shown). The welder strikes an arc by touching or scraping electrode 10 against workpiece 14 to close a circuit between electrode 10 and work clamp 24. As electrode 10 is drawn away from workpiece 14, an arc 12 is initiated. The welder then feeds a bare welding rod 26 to welding site 22, thereby creating a molten puddle 28. Molten puddle 28 hardens to leave a weld bead 30 joining two pieces of metal.
Numerous problems persist with this physical method of striking an arc because the tip of the tungsten electrode usually breaks off due to touching or scraping the electrode against the workpiece. Often, the tip falls into the molten puddle and contaminates the weld. Also, the welder must then resharpen or replace the electrode. Not only does this process inconvenience the welder, but it also wastes time and resources, which ultimately imparts a higher cost to each weld.
One known solution is to use a copper plate to strike the arc. The plate is placed on the workpiece alongside the weld and used to strike the arc, after which the arc is moved to the proper welding location to begin welding. Though the copper plate tends to reduce the frequency with which the electrode will break, breakage still occurs because the electrode is struck against a metal. Also, the manipulation of a copper plate near the weld site can become cumbersome for the welder, adding to welder fatigue and reducing productivity.
To address these problems, arc starter circuits, such as circuits which produce high frequency pulses, have been designed to electronically initiate the welding arc. In such known arc starter circuits, a preflow of protective gas is allowed, followed by the simultaneous initiation of an arc starting signal along with enablement of output current flow. It has been found, however, that this method of arc initiation does not reliably start the arc.
Accordingly, what is needed is an improved method and apparatus for initiating a welding arc to overcome the problems and limitations of the prior art.